This invention relates to a method for synthesizing musical tones by using a modulation operation such as a frequency modulation operation or an amplitude modulation operation and, more particularly, to a method for synthesizing musical tones capable of controlling a complicated waveshape by a simple operation.
A basic system for generating a tone signal having desired overtone composition by using a frequency modulation (hereinafter abbreviated as FM) operation of an audio frequency range is disclosed in U.S. Pat. No. 4,018,121. A similar system generating a tone signal by performing a similar FM operation by using a waveshape containing abundant harmonic components (e.g., a saw tooth waveshape) is disclosed in Japanese Patent Publication No. 7570/1979 (corresponding to U.S. patent application, Ser. No. 922,883 filed on July 7, 1978, now U.S. Pat. No. 4,643,066. Further, a basic system for generating a tone signal having a desired overtone composition by using an amplitude modulation (hereinafter abbreviated as AM) of an audio frequency range is disclosed in Japanese Patent Publication No. 29519/1983 (corresponding to U.S. patent application Ser. No. 66,285 filed on Aug. 13, 1979, abandoned).
In the above described prior art systems, however, a simple monomial modulation operation is insufficient for synthesizing a satisfactory tone color having sufficient harmonic components and a complicated modulation operation of a multiplet or polynomial operation is required. This necessitates a complicated and large operation circuit and, in a system in which operation of each operation term is performed on a time shared basis, requires increase in the speed of the control clock with a resulting increase in the manufacturing cost. As a method for synthesizing a tone containing abundant harmonic components by a relatively simple operation, a method using a waveshape containing abundant frequency components as a modulating wave or carrier wave has been conceived as disclosed in the above mentioned Japanese Patent Publication No. 7570/1979. Since, however, the waveshape available for the operation is limited to the one or ones stored in the memory, tone colors which can be synthesized have been limited to a narrow range.